When such components, generally called "solar cells", make use of one species only of semiconductor material (usually silicon or Gallium arsenide) they cannot achieve best transformation of the light energy in solar radiation because of the spread of the solar spectrum. A given semiconductor material has a forbidden band of determined width, such that photons having smaller energy than said bandwidth are not absorbed and therefore cannot generate the electron-hole pairs required for producing photocurrent. Conversely, photons having energy greater than that of the forbidden band will indeed create electron-hole pairs, but with excess energy relative to the energy of the forbidden band, which excess is converted into heat and not into electrical energy.
To improve solar energy conversion, proposals have been made to associate in various configurations a plurality of different semiconductors having forbidden bands of different widths. Such components are called "multispectral solar cells".
The present invention relates to one of the proposed configurations, known as a "stacked" configuration which involves preparing two (or more) different cells each on its own substrate and then in superimposing the cells by fixing them together with a transparent adhesive. The adhesive may be conductive, thereby enabling two cells to be connected in series (but in that case the photocurrent produced by the device is limited to the lowest photocurrent that is generated), or else the adhesive may be insulating, with each of the cells then being provided with its own electrodes that are separately connected to distinct circuits of the electronics in the charging system (which must therefore be designed accordingly).
That configuration suffers from a certain number of drawbacks, in particular the fact that since the two cells have to be made separately, the final component has two thicknesses of substrate, thereby increasing both the weight and the cost of the structure correspondingly, particularly when stacking a GaAs cell (or a fortiori an InP cell) on a silicon cell: the heavier and more expensive GaAs substrate is not used for mechanical support and it plays no active role. It is indeed possible to thin this layer down by lapping, thereby reducing the weight of the cell, but that further increases cost, since the material removed by lapping is not recoverable and the additional lapping step contributes to increasing the final production cost of the component.